1. Technical Field
The present application relates to integrated circuits, and more specifically to charge pump circuitry used in integrated circuits.
2. Related Art
Integrated circuits, sometimes referred to as microchips or semiconductor devices, are in widespread use and can be found in almost all electronic equipment in use today. A typical integrated circuit will include a pin for receiving an external supply voltage VDD that is predetermined and configured to remain at an at least somewhat constant voltage level during operation. However, some integrated circuits are configured to use one or more voltage levels that exceed the supply voltage VDD for at least some operations. For example, some integrated circuits are memory devices that use a voltage greater than supply voltage VDD for read and/or write operations.
Such integrated circuits will often include one or more charge pumping circuits. A charge pumping circuit is a circuit that can provide a voltage that exceeds the supply voltage VDD. For example, in some flash memory devices, a drain pump circuit is used for providing high voltages for hot-electron programming. A drain pump circuit is a type of charge pumping circuit and typically includes several large pumping capacitors. Also, in some flash memory devices, a standby wordline (WL) voltage is maintained above VDD in order to provide for faster read operations. A sustained capacitance helps to maintain this standby WL voltage. The sustained capacitance can be provided by elements of the memory array, but sometimes the memory array does not provide sufficient sustained capacitance. In such cases, additional capacitance can be added to the peripheral area of the memory chip. However, one of the important goals for integrated circuit designers is to reduce the die size in order to reduce fabrication costs. Thus, the addition of capacitors to the peripheral area of a memory chip runs counter to the desire to reduce the die size and fabrication costs.
Thus, it is desirable to find alternative approaches for providing acceptable levels of sustained capacitance while reducing the die size and fabrication costs of integrated circuits, particularly those comprising electronic memory devices.